This invention relates to an underground storage tank and more particularly to an underground storage tank for use in storing liquids safely under a variety of conditions for extended periods of time.
Today there are hundreds of different chemicals stored literally in thousands of underground tanks, such as fuel oils, lubricants, gasoline, and other chemicals some of which are highly toxic or explosive and a direct threat to persons and property once out of their tanks. In many cases, the tanks have been in place for thirty years of longer.
The typical tank which has been used for such storage is made out of steel. Although steel tanks can be designed with cathodic protection, such design does not prevent corrosion from soil pH, de-icing salts, runoff from septic tanks, internal rust on the inside of the tank, or rust between the wall of double wall tanks due to condensation. As a result, there has been a steady growth in the incidence of tank failure resulting in leaks many of which have the capability of damaging the environment and contaminating underground water supplies as well as causing injury to the property of home owners, businesses, and the general public.
The problem is especially acute for tanks in which petroleum products are stored as such products contain a number of carcinogenic compounds such as benzine, zyline, and toluene. This problem is experienced throughout the world and is not limited to the United States.
If leaking and overage tanks are merely replaced by tanks of the same or similar design then of course the problems mentioned above are merely programmed for recurrence.
There have been efforts to improve underground tank design to avoid or minimize some of the problems mentioned above, and consequently tanks made out of fiberglass reinforced plastic (FRP), such as used in the manufacture of boat hulls, and which may be referred to hereinafter merely as fiberglass, have come into some use due to the resistance of this material to corrosion.
The steel tank typically is cylindrical in configuration, and fiberglass has been substituted for steel while retaining the cyclindrical shape. But the mere substitution of fiberglass for steel in the construction of such tanks has introduced a whole set of new problems. Present design of tanks made of fiberglass tend to be fragile and are highly susceptible to damage during shipping and installation. The cylindrical tank made out of fiberglass performs underground like a flexible conduit and relies on the surrounding soil to maintain its shape. If not evenly backfilled a tank of such design can collapse therefore requiring a very careful and expert installation which increases the cost of installing such tanks.
In addition, according to studies by the EPA, about 70% of reported tank leaks are due to failures in piping or pipe fittings so that substitution of fiberglass for steel in the wall construction would only reduce the incidence of leaks in the remaining 30% of reported tank leaks as the piping and fittings can not be made out of the fiberglass.
U.S. Pat. Nos. 1,336,439, 2,056,179, 2,736,449, 3,776,414, 4,557,199, and 4,685,585 show typical undergound tank designs pertinent to, but lack teachings of, the present invention.